1. Field of the Invention
The present invention relates generally to conferencing systems, and more particularly to daisy chained conferencing systems.
2. Description of the Related Art
Table-top conferencing systems have become an increasingly popular and valuable business communications tool. These systems facilitate rich and natural communication between persons or groups of persons located remotely from each other, and reduce the need for expensive and time-consuming business travel.
In conventional conferencing systems, a single conferencing device is located at each site, for example, inside a conference room. Participants gather around the conferencing device to speak into a microphone and to hear the far-side participant on a loudspeaker. The acoustic properties of the conference room play an important part in the reception and transmission of audio signals between the near-end and the far-end participants. Reverberation is one of several undesirable physical phenomena degrade inter-device communications.
Reverberation is caused by the existence of multiple paths of multiple lengths between the sound source and the sound receiver. The multiple paths are formed due to reflections from the internal surfaces of the room and the objects enclosed therein. For example, in addition to the direct path from the source to the receiver, there may be paths formed by the sound reflecting from each of the six internal surfaces of a room. The auditory consequence of this phenomenon is experienced when the sound of a source persists for a certain amount of time even after the source is cut off. Reverberation's impact on speech is felt when the reverberation of a first syllable persists long enough to overlap with the subsequent second syllable, possibly making the second syllable incomprehensible. One way to reduce reverberations is to cover the reflective surfaces inside the room with materials having high absorption coefficient. However, this is expensive and may not be feasible when the portability of the conferencing devices is taken into account.
A single conferencing device may provide only one or three microphones to receive the voices of all the participants. This exacerbates the reverberation problem. Microphone pods may be connected to the main speakerphone, thus allowing microphones to be closer to the speakers—somewhat alleviating the reverberation problem.
Further, a single conferencing device generally provides only a single loudspeaker at a single location. If the distribution of positions of participants is uneven with respect to the position of the conferencing device, the participants farthest from the device may hear the sound of the loudspeaker at a much lower level than the participants nearer to the device. This non-uniform sound distribution puts undue constraints on the positions of the participants. In some scenarios, where the conference device is operated in a large room or auditorium, the non-uniform sound distribution may render the sound from the loudspeaker imperceptible, or even inaudible, to some participants. The microphone pods used above to reduce reverberation problems do nothing to address this problem.
Furthermore, a single conferencing device generally provides only a single location to control the operation of the conferencing device. The user interface mounted on the conferencing device may not be easily accessible to participants that are positioned far away from the conferencing device. For example, functions like dialing, muting, volume, etc., which may be quite frequently used by the participants, may not be easily accessible to all participants. This lack of ease in accessing the user control functions on the conferencing device may also put constraints on the positions of the participants.
*Certain conferencing devices may act as a bridge to allow simultaneous connectivity to multiple communication devices. *One or more communication devices, when connected to a bridge, transmit and receive audio signals to each other via the bridge. The bridge is required to process the audio signals associated with each communication device participating in the conference. The processing typically includes mixing, audio conditioning, amplification, etc. With large number of communication devices, the processing may require higher bandwidth and lower processing latency that that provided by a single conferencing device acting as a bridge. As a result, bridges are generally relatively expensive devices. One could attempt to combine many different locations by having a number of participants act as small bridges using three-way conference calling features commonly available on office PBX systems. However, this is difficult to coordinate and usually results in very uneven speaker levels.
It would be desirable to provide a system to provide better loudspeaker distribution with minimal reverberation problems. It would also be desirable to provide satisfactory bridging capability at a lower cost than conventional bridges.